LM350t - Electronic Circuits Projects Diagrams Free

Voltboy · 30th November 2007, 03:43 AM

Hello guys.
I just got a new LM350t and want to use it properly.
The formula for Vout is = 1.25(1+R2/R1)+Iadj R2
I just didn't understood what is Iadj. Could someone explain me what is it?
Here is the datasheet
I'm trying to do the circuit on figure 13

OutToLunch · 30th November 2007, 04:01 AM

Iadj is current that comes out of the ADJ pin (see the third line of the electrical characteristics table). This current will flow through R2, which will yield a voltage. It isn't much - 50uA, typically - so it won't have to much effect - unless you use resistor values that are huge.

Voltboy · 30th November 2007, 04:28 AM

Oh.. thanks
I want to get 5v so here is my equation.
Vout=1.25(1+R2/R1)+Iadj R2
Vout= 1.25(1+713/240)+(0.000005*713)
Vout= 4.9671
I think I did it right and I guess 4.96 is pretty near 5.
I put up 713 ohm cuz i dotn have a really good selection of resistor and using about 2 resistor it is best I can get (680+33).
Thanks

audioguru · 30th November 2007, 09:57 PM

Look in the datasheet.
240 ohms is used as R1 in the more expensive LM150 circuit. Use 120 ohms for the LM350 so the output voltage doesn't rise when there is no load current.

If R1 is 120 ohms and R2 is 360 ohms then the output is very close to 5V.
Or use 100 ohms and 300 ohms. They are all standard 5% values.

Voltboy · 30th November 2007, 10:06 PM

Well I got 20 ohm, 33ohm,82ohm,68.1ohm,150 ohm and 330 ohm. I can get 363 ohms and 115ohm.
I will try with those.
But still, the one I made with 240 ohms and 713 ohms got to 5.06v with a LED.

audioguru · 30th November 2007, 10:12 PM

ICs are not all made the same. There are good ones and not so good ones which explains the wide range of spec's in the datasheet.

Maybe the factory had a good production yield so most were like the more expensive LM150. Then you are lucky.
But the production yield next week might be lousy and the LM350 ICs will have their minimum (or maximum) spec's.

Voltboy · 30th November 2007, 10:23 PM

Then I'm lucky

Hero999 · 1st December 2007, 04:07 PM

The 120

hm: resistor is only use to satisfy the minimum load requirement for the IC. If you're going to have a 10mA load on the output (like an LED) then it doesn't matter, you could use a 240k resistor if you wanted but you'd need to take Iadj into account.

Have you tried measuring the voltage with the LED disconnected?

It might read >5.06V if you have a not so good regulator.

audioguru · 1st December 2007, 05:12 PM

The 120 ohm resistor value is needed for some LM3xx regulators and only when the input voltage is high and there is no other load current. I use 120 ohms or less for all my LM3xx circuits.

Voltboy · 2nd December 2007, 12:40 AM

Well, I fixed the regulator as you said and got about same results. I'm gonna let it with the resistors you said.

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LM350T as Current Source	abbarue	Electronic Projects Design/Ideas/Reviews	1	14th October 2007 11:26 PM

30th November 2007, 03:43 AM	(permalink)
Voltboy	LM350t Hello guys. I just got a new LM350t and want to use it properly. The formula for Vout is = 1.25(1+R2/R1)+Iadj R2 I just didn't understood what is Iadj. Could someone explain me what is it? Here is the datasheet I'm trying to do the circuit on figure 13 __________________ The best e-book AAC Last edited by Voltboy; 30th November 2007 at 04:16 AM.

30th November 2007, 04:01 AM	(permalink)
OutToLunch	Iadj is current that comes out of the ADJ pin (see the third line of the electrical characteristics table). This current will flow through R2, which will yield a voltage. It isn't much - 50uA, typically - so it won't have to much effect - unless you use resistor values that are huge.

30th November 2007, 04:28 AM	(permalink)
Voltboy	Oh.. thanks I want to get 5v so here is my equation. Vout=1.25(1+R2/R1)+Iadj R2 Vout= 1.25(1+713/240)+(0.000005*713) Vout= 4.9671 I think I did it right and I guess 4.96 is pretty near 5. I put up 713 ohm cuz i dotn have a really good selection of resistor and using about 2 resistor it is best I can get (680+33). Thanks __________________ The best e-book AAC

30th November 2007, 09:57 PM	(permalink)
audioguru	Look in the datasheet. 240 ohms is used as R1 in the more expensive LM150 circuit. Use 120 ohms for the LM350 so the output voltage doesn't rise when there is no load current. If R1 is 120 ohms and R2 is 360 ohms then the output is very close to 5V. Or use 100 ohms and 300 ohms. They are all standard 5% values. __________________ Uncle $crooge

30th November 2007, 10:06 PM	(permalink)
Voltboy	Well I got 20 ohm, 33ohm,82ohm,68.1ohm,150 ohm and 330 ohm. I can get 363 ohms and 115ohm. I will try with those. But still, the one I made with 240 ohms and 713 ohms got to 5.06v with a LED. __________________ The best e-book AAC

30th November 2007, 10:12 PM	(permalink)
audioguru	ICs are not all made the same. There are good ones and not so good ones which explains the wide range of spec's in the datasheet. Maybe the factory had a good production yield so most were like the more expensive LM150. Then you are lucky. But the production yield next week might be lousy and the LM350 ICs will have their minimum (or maximum) spec's. __________________ Uncle $crooge Last edited by audioguru; 1st December 2007 at 12:04 AM.

30th November 2007, 10:23 PM	(permalink)
Voltboy	Then I'm lucky __________________ The best e-book AAC

1st December 2007, 04:07 PM	(permalink)
Hero999	The 120hm: resistor is only use to satisfy the minimum load requirement for the IC. If you're going to have a 10mA load on the output (like an LED) then it doesn't matter, you could use a 240k resistor if you wanted but you'd need to take Iadj into account. Have you tried measuring the voltage with the LED disconnected? It might read >5.06V if you have a not so good regulator. __________________ I also post at the following sites: http://www.stop-microsoft.org http://www.heated-debates.com Screen name: Aloone_Jonez

1st December 2007, 05:12 PM	(permalink)
audioguru	The 120 ohm resistor value is needed for some LM3xx regulators and only when the input voltage is high and there is no other load current. I use 120 ohms or less for all my LM3xx circuits. __________________ Uncle $crooge

2nd December 2007, 12:40 AM	(permalink)
Voltboy	Well, I fixed the regulator as you said and got about same results. I'm gonna let it with the resistors you said. __________________ The best e-book AAC Last edited by Voltboy; 2nd December 2007 at 01:08 AM.